Urea-formaldehyde primary alkylene diamine condensation products



Patented Feb. 2, 1954 UREA-FORMALDEHYDE PRIMARY ALKYL- ENE DIAMINE CONDENSATION PRODUCTS William Robert McClellan, Kennett Square, Pa.,

assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware N Drawing.

Application April 7, 1950,

Serial No. 154,727

. 14 Claims. 1

This invention relates to urea-formaldehyde condensation products and, more particularly, to diamine-modified urea-formaldehyde resins having improved properties and to a process of preparing same.

Urea-formaldehyde resins are commercially important thermosetting plastics but the hitherto known resins of this type possess the serious defect of low water resistance. This defect makes them unsuitable for use outdoors or in other applications involving exposure to severe conditions of moisture.

An object of the present invention is to provide urea-formaldehyde condensation products having outstandingly high Water resistance and an economical and feasible process of preparing same. A further object is to provide such condensation products having rapid curing rate and good flow characteristics in molding and which give molded products possessing good toughness, high heat distortion temperatures, and excellent resistance to crazing and loss of toughness on exposure outdoors or to heat.

The above objects are accomplished according to the present invention by the formation of a condensation product of reactants essentially consisting of urea, and, per mole of urea, 1.5 to 2.5 moles of formaldehyde, and 0.03 to 0.12 mole of a primary alkylene diamine containing from 4 to carbon atoms, inclusive, and in which the primary amino groups are separated by at least 4 carbon atoms, and an acid catalytically active for the condensation of urea with formaldehyde in an amount stoichiometrically equivalent to 2.5% to 12.5% of the diamine. These new condensation products are prepared by heating at a temperature not exceeding 85 C. in an aqueous medium the above reactants until a clear, homogeneous solution having a pH between 5.0 and 6.5 is obtained. Thereafter the resulting resin may be dried at a temperature below 100 C.

Preferably, the condensation product is formed from reactants essentially consisting of urea and, per mole of urea, 1.6 to 2.0 moles of formaldehyde, and 0.06 to 0.09 mole of hexamethylenediamine, and p-toluenesulfonic acid in an amount stoichiometrically equivalent to 2.5% to 12.5% of the hexamethylenediamine.

A preferred way of carrying out the process of this invention is to heat to about 50 C. an aqueous mixture of urea and formaldehyde, or equivalent amounts of water-soluble monomeric condensation products of urea and formaldehyde, e. g., monomethylolurea, dimethylolurea or higher methylolureas,- the mixture containing at least 15% water by combined weight of urea and formaldehyde. The hexamethylenediamine or other diamine is then added to the mixture with agitation and, preferably after the precipitate thereby formed is broken up to eliminate large agglommerates, the p-toluenesulfonic acid, sulfuric acid, or other acid is added and the temperature of the reaction mixture raised to about C.-75 C. Heating is continued at that temperature until a clear solution having a pH between 5.0 and 6.5 is formed.

If desired, all the reactants may be added substantially simultaneously but it is preferred to mix them in the sequence above. The reaction mixture is alkaline at the start, the pH ranging up to as high as 9 to 12 depending upon the amount of diamine present, due to the excess of diamine over acid catalyst, and, as indicated, it contains a precipitate at the start. As the reaction proceeds, the pH of the mixture gradually decreases and the precipitate dissolves due to the reaction of the diamine with the urea: formaldehyde resin. It is essential in order to obtain a resin having the outstanding properties mentioned previously, that the reaction be continued until the mixture is homogeneous and clear and has a pH between 5.0 and 6.5. The resulting solution, which shows no evidence of any appreci able increase in viscosity, may be converted to a molding compound by incorporating in it a quantity of a cellulose filler, e. g., alpha-cellulose,- amounting to 20%-50%, preferably 25%l0%, by weight of the finished molding compound, and then drying the mixture at temperatures of 50 C. to 100 (2., preferably under reduced pressure. The cellulose filled resin compositions of this invention may be dried at higher temperatures than those (50 C.55 C.) normally used in drying conventional urea-formaldehyde compositions. The time of drying varies with the temperature and pressure being used, the lower temperatures and higher pressures naturally requiring longer times. At C.- C. and pressures of 20-40 mm. of mercury, drying times of 16 to 24 hours are satisfactory. Pressures from,

atmospheric pressure down may be used but it is not necessary to go below 5-10 mm. of mercury to obtain practical drying rates.

Where the resin is to be converted into a molding compound, it is preferred that its pH shall be in the lower part of the specified range of 5.0-6.5, e. g., about 5.0-5.5 and at least not above a pH of 6.0. Rather than continue heating thereaction mixture until'the pH reaches 6.0 or lower, the heating may be terminated when the pH of the reaction mixture enters the top part of the range 5.0-6.5, and further acid may then be added to bring the pH down to 5.5 or so. Molding compounds having better flow character istics result-fromtheresin having a pH not above 6.0 andit immaterial whether the pI-I is adjusted to that level by continued heating of the reaction mixture or adding further acid after taining water), 6.4 parts of urea, 6.5.parts of a 75% aqueous solution of hexamethylenediamine, 125 parts of water, and 0.6 part of ptoluenesulfonic acid, added in the orderlisted; is heated with stirring to a temperature of 73 C. After; b'eingmeld at this" .temperature. for five minutes,.there isobtained a. clear solutionhaving a: pH of 6.5; To the'rresin solution thus formed, ,there are added: 3 parts of. a 1% aqueous solution of hydrochloric acid which lowersthepl-I of. theesolution" 130:6.0:v This solution is then mixeds-uniformly-with parts of 4 alpha-cellulose asrafiller-"and the resulting. mixture is dried in a vacuum :oven at=70 C. under apressure of about -min. of mercury; for 24hours. The yield of dry product amounts to 72 parts, of which 20 parts; is filler and 50- parts ismodified ureaformaldehyde:resinxcontaining 9.4% of chemica1lybound hexamethylenediamine;

In.- this example. there was used, per mole. of urea, 1.6. moles1of formaldehyde, and 0.08 mole of hexamethylenediamine. The quantity of ptoluenesulfonic. acid: was stoichiometrically equivalent1to.4.0% of the hexamethylenediamine.

The: product oftEXarnpleI exhibits excellent flow characteristics, when molded at a temperature-of. 140?*C. under a-pressure of 4,000 lb;/sq; in. with a: molding; cycle of 5. minutes. The molded product istranslucent and it has excellent toughness. and resistance to: boiling water; Molded: barsof this resin are capable of withstandingemore than-soyclesof alternate immersionfor: 1.to 2 hours in-boiling: water followed by( drying. inainfor. 24 hours without showing any, evidence of .c-razing. orcracking. Ifhe molded resinalso. hasra heat distortiontemperature; as determined by, ASTM method D-648, of 152 C. Moldedbars ofresinsa of this type have flexural strengths of about 15,600 lb./sq; in.-, and after 8 'cycles-.of "alternate immersion in boiling water: andlair drying; still. have flexura'lstrengths of. about.12,500 =lb;/sq.- in.

EXAMPLE II A mixtureioil20parts of dimethyloiurea; (0011"- taining;.15% .water-), IZi-Spartsof:urea, 6.5' parts of. a 75% aqueous: solution: of hexamethylenediamine; 250 parts'ofiwater, 1.2.partsof p.-toluene-- sulfonic acid, addeddn the above order, isheated toa temperature of'lfl C.72 C., and held at this temperature for minutes. The resultingclear solutionhas a-pH:of.-6.0 and is mixed thoroughly with 40 parts of alpha-celluloseand dried at 70 C. undera pressureof 23 mm.- ofmercury for 24 hoursi The resulting. dryproduct amounts to 140lparts..

In this: examplethere wasused, per mole. of

urea,.1.6.mo1es-of. formaldehyde, and.0.04. mole.

offhexamethylenediamine. The. quantity of p:- toluenesulfonic acid was. stoichiometrically.

equivalent to 4.0% of the hexamethylenediamine.

The product of Example II exhibits good flow when molded under 1,000 Ila/sq. in. pressure at 140 C. The molded product has a heat distortion temperature of 144? C. and. a fiexural strength of.14,000 lb./sq. in. It also has good water resistance, being capable of withstanding more than 8 cycles of alternate immersion in boiling water and drying in air. After 8 such cycles,1the'=test" specimen still has a flexural strength of 10,600 lb./sq. in.

EXAMPLE III A mixture:of,4=8;parts of urea, 104 parts of a 37% aqueous formaldehyde solution, 5.6 parts of tetramethylenediamine, 25 parts of water, and 0.9. partof p toluenesulfonic acid, added in the above order, is heated with stirring to a temperaturer-ofi'lm'C. and held at this temperature for a period of 45 minutes. The resulting clear solution hasa pl-I of 6.4.. This solution ismixed-uniformlys with 34. parts i of alpha-cellulose. filler and themixture is. dried in. an oven at 70 C. under apressure of I 23- mm. of mercury for 24 hours. There is obtained parts otdry prod-- not.

In this. example-there was used, per mole of urea, 1.6.moles otformaldehyde, and.0.08 mole of tetramethylenediamine. The quantity of, p-toluenesulfonic acid was stoichiometrically equivalent to 4.1% otthe tetramethylenediamine.

When the product of Example III-ismoldedat C.,.the compositionhas excellent fiowat 500 lb./sq. in. pressure. The molded article. has aheat distortion temperature-of 110 C. anda flexural strength of. 16,400 lb./sq. in. The molded product doesnot. show failure. after 5 cycles. of alternate immersion in. boiling water andair drying.

EXAMPLE IV The process of Example 111' is repeated with the exception that the tetramethylenediamine of. that example is. replacedby 9.2; parts of decamethylenediamine and the reaction mixture is heated at 76C. instead'of 70 C. Under these conditions there is obtained in l5,minutesa clear. solution having av pH of 5.8. Thissolutionis mixed with alpha-cellulose. filler and dried as described in Example III. The resulting. dried product amounts to 112' parts.

In this examplethere was used, per. mole of. urea, 1.6 moles of formaldehyde, and0.067 mole of decamethylenediamine. The. quantity of ptoluenesulfonic acid was stoichiometrically equivalent to,4;9% of the.decamethylenediamine.

When theproduct of Example IV is moldedat' 140 C1, the composition hasexcellent flow at. a. pressure of 2000 lb./sq. in. Themoldedarticle has a heat distortion temperature. 05124.? C.,,a flexural strength. of 14,000. lb./sq. in., and. is. capable of withstanding, more. than. 8.. cycles. of

alternate immersion in boiling water and. airy drying."

EXAMPLE V The vresultingsolution isclear and homogeneous:

and has at pI-Lof. 6.5. This. solutionis uniformly mixedwith 3e .partsof alpha-cellulose. filler .and. the .mixtureis dried. at..70. C. under. apressureof;

5. 23 mm. of mercury for 24 hours. The dried product obtained amounts to 107 parts.

In this example there was used, per mole of urea, 1.6 moles of formaldehyde and 0.08 mole of 2,5-dimethyl-1,6-hexanediamine. The quantity of p-toluenesulfonic acid was stoichiometrically equivalent to 4.05% of the 2,5-dimethyl-L6-hexanediamine.

When the product of Example V is molded at 140 C., the composition has excellent flow under a pressure of 2,'000 lb./sq. in. The molded article has a heat distortion temperature of 117 C; and is capable of withstanding more than 8 cycles of alternate immersion in boiling water and air drying.

EXAMPLE VI This example illustrates the preparation of a resin having a ratio of 1.75 moles of formaldehyde per mole of urea and 0.10 mole of hexamethylenediamine per mole of urea, in the presence of an amount of p-toluenesulfonic acid corresponding to of the diamine equivalent. Nine hundred parts of urea moles) and 2130 parts of 37% aqueous formaldehyde (26.25 moles) are mixed together. The solution is then heated to 50 C. and 232.5 parts of a 75% aqueous solution of hexamethylenediamine (1.5 moles) added while agitating vigorously with a mechanical stirrer to break up the precipitate which forms. A solution of 28.5 parts of ptoluensesulfonic acid (0.15 mole) in 25 parts of water is added to the solution, which is then heated to 70 C.-'75 C. After 15-30 minutes the precipitate dissolves giving a clear solution. Heating is continued until the pH of the solution reaches 6.0 to 6.5, a period of about 75 minutes after the addition of the acid catalyst being required. The resulting solution is cooled to 30 C.40 C. and adjusted to a pH of 5.5 by the addition of dilute sulfuric acid and poured over 750 parts of alpha-cellulose. The resin solution and cellulose filler are thoroughly mixed and vention broadly comprises a condensation product of reactants essentially consisting of urea, and, per mole of urea, 1.5 to 2.5 moles of formaldehyde, and 0.03 to 0.12 mole. of a primary alkylene diamine containing from 4 to 10 carbon atoms, inclusive, and in which diamine the primary amino groups are separated by at least four carbon atoms, and an acid catalytically active for the condensation of urea with formaldehyde in an amount stoichiometrically equivalent to 2.5% to 12.5% of the diamine.

While the examples illustrate the invention by the use of certain specific diamines as the modifying agent, any primary alkylene diamine having from 4 to 10 carbon atoms, inclusive, with at least 4 carbon atoms separating the amino groups may be used. Among the other alkylene diamines suitable for use in the present invention are pentamethylenediamine, heptamethylenediamine, octamethylenediamine, 3-methyl 1,6-hexanediamine, nonamethylenediamine, and E-methyl-1,9-nonanediamine. Since the most desirable combination of properties of the resulting diamine-modified urea-formaldehyde resins are obtained with hexamethylenediamine, this particular diamine is especially preferred. The chain length of the alkylene diamines is a critical factor in obtaining the improved resins of this invention. Alkylene diamines having more than 10 carbon atoms are not suitable for -use in preparing the modified urea-formaldethen dried in a tray in a vacuum oven at 70 C.- I

75 C. for 16-20 hours. The final product amounts to 2316 parts.

A portion of the cellulose-filled resin prepared above is ground in a ball mill to a fine powder and then compression molded at 2000-3000 lb./sq. in. at 140 C.150 C. for 4-5 minutes into test bars. These bars have the following properties: heat distortion temperature (264 lb./sq. in.) 138 C., 145 C., Izod impact strength 0.31 lb./inch of notch, a fiexural strength of 15,200 lb./sq. in., and are capable of withstanding more than 22 cycles of alternate immersion in boiling water and drying in air. Test bars submitted to 22 such cycles of boiling and drying still have a flexural strength of 14,900 lb./sq. in., this corresponding to 98% retention of flexural strength. A mixture of 895 parts of the resin solution prepared above, 4.5 parts of zinc stearate and 35.8 parts of titanium dioxide pigment are milled in a two roll mill to form a hard sheet. This sheet is broken up and ground to pass a A." screen. The granular product obtained has a bull: density of 0.68 g./cc. and when molded in an impact bar mold forms excellent bars at 500 lb./sq. in. pressure at 140 C. for 5 minutes. The resulting bars have a heat distortion temperature of 138 C. The granular resin also has excellent dew and gives good moldings an ASTM mobility cup mold. It will be understood are. merely illustrative and that the present in-' that the above examples hyde resins. Diamines having less than 4 carbon atoms give products having greatly inferior properties. In particular if ethylenediamine is substituted for an alkylene diamine having from 4 to 10 carbon atoms in the process of this invention, products lacking in water resistance and having low heat distortion temperatures and toughness (fiexural strength) are obtained. More specifically, a resin prepared from urea and formaldehyde in the proportions of 1.6 mole of formaldehyde to 1 mole of urea, 0.08 mole of ethylenediamine per mole of urea and p-toluenesulfonic acid (in an amount stoichiometrically equivalent to 5% of the ethylenediamine) as catalyst by heating at 70 C. until a clear solution having a pH of 6.5 is obtained and then mixed with 23 parts of alpha-cellulose filler, r ied at 70 C. and molded at C. under 500 lie/sq. in., has the following properties: Heat distortion temperature, 83 C.; crazing and deterioration pronounced after only one cycle of alternate immersion in boiling water and air drymg.

The proportion of the primary alkylene diamine used is also a critical factor in producing the improved resins of this invention. An

amount-of such diamine less than 0.03 mole per mole of urea gives a product having poor flow during molding and the molded articles do not possess the desired high water resistance. An amount greater than 0.12 mole of diamine per mole of urea gives products which are inferior in their heat distortion temperatures, stiffness and water resistance. Products having the optimum combination'of properties are obtained when proportions of alkylene diamine ranging from 0.06 to 0.09 mole of diamine per mole of urea are employed.

The specific acid, p-toluenesulfonic, acid mentioned in the examples is the preferred catalyst for use in the process of this invention since it highlyysuitable. ,-However, other organic orx in- 7*. organic acidsxcanbausedii desired; Examples of other catalytically activev acids; which pro,- duce products having properties superior to conventional urea-formaldehyde resins, include g-lycolic and phthalic acids; Still other acids which are catalyticallyactiveinclude oxalic, phosphoric, and citric acids. Although theteffectiveness of these acids as catalysts. is not directly proportional to their dissociation constants, the acids which are catalytically active in general have dissociation constants greater than 1.0 10 at 25 C.

The acids effective in this process must be used in the proportions specified, i. e., from 2.5% to: 12.5% of the amount stoichiometrically equivalent to the diamine present. With this proportion of acid the reaction mixture is initially alkaline, the pH usually being from about 9 to. about 12 at the beginning of the reaction, and as the condensation proceeds the pH decreases. The condensation must be continued until: a pH between 5.0 and 6.5 is reached. It is: essential that the pH of the final reaction mixture be within these limits to produce resins having the superior properties mentioned previously. As indicated before, it is permissible to heat the reaction mixture only until the pH thereof enters the pH range of 5.0-6.5 and, in order to obtain a pH in the lower part of the range, to add further acid rather than prolong the heating. This is a preferred expedient'where the resin is to be converted to a molding compound since a resin having a relatively low pH of. 5.0 to 5.5 is usually more desirable for such use.

If an amount of acid catalyst substantially more than 12.5% of the diarnine equivalent is employed in the process of this invention or if the condensation is continued to a pH below 5.0, the resulting resins have poor flow characteristics on molding, and the molded articles have poor water resistance. If less than 2.5% of acid is used or if too weak. an acid is used, the reaction mixture cannot be brought to a pH of less than 6.5 and as a result the product also has inferior properties, e. g., poor curing on molding and the molded article has inferior toughness, water resistance and heat distortio temperature.

The urea and formaldehyde are reacted in the ratio of 1.5 to 2.5 moles of formaldehyde per mole of urea. Within this range more specificranges may be somewhat preferable in producing a resin designed for a particular use. In the preparation of a resin to be converted to a molding compound, by way of illustration, it is preferred but not necessary to use 1.6 to 2.0 moles of formaldehyde per mole of urea. It is not essential to use urea and formaldehyde as distinguished from equivalent amounts of watersoluble monomeric condensation products of urea and formaldehyde, e. g., methylolurea, dimethylolurea, or higher methylolureas, provided that the essential proportion range of urea and formaldehyde is observed.

The temperature at which the reaction may be; carried out can be varied over a considerable range. It is not advisable to exceed 85 C. appreciably while, at the other extreme, temperatures below 35 C. are not practical as the reaction proceeds: too slowly. It is preferred to use a temperature in the upper part of this range and reactiontemperatures of 65 C. to '75' C1. are; especially favorable.

The proportion of: waten'present. thee re'-l5i the2cellulose-fi1ledresinsof thisinvention-retam action mixture. is not sharply? critical; although the use of less than 15%; by weightofthe com,- bined urea and. formaldehyde; is. not desirable. Excellentresults have been obtained with 20% to 25% water by. weight of the combined urea and formaldehyde but higher proportions; of water are entirely operative and simply involve the handling of greater amounts of water. than there is any real need to use.

In addition to alpha-cellulose, the. diaminemodified urea-formaldehyde resins of this in.- vention can be filled' with other materials in a wide range of proportions. Examples of other suitable fillers include other types of cellulose such as wood floor, asbestos, and other: typesof resins. However, cellulosic fillers are preferred since this type of filler gives the best molding characteristics and the molded products possess an excellent combination of properties. Amounts of cellulosic fillers ranging from 25% to 40% of the total composition give exceptionally good results.

The urea-formaldehyde resins of this invention may, if desired, be colored by conventional pigments. Similarly, other conventional resin modifiers may be incorporated with the ureaformaldehyde resins of this invention. A specific example of such modifiers is a mold lubricant such as zinc stearate.

The excellent combination of properties possessed by the resins of this invention makes them very suitable for use in all applications for which thermosetting resins are required. The outstanding water, heat and light resistance of the resins of this invention makes them especially useful in those applications where the resins must be subjected to relatively-moist conditions or to exposure out of doors.

The condensation products of this invention containing formaldehyde and urea in the molar ratio of 1.6-2.0 to l and containing a cellulosic filler are especially valuable as molding compositions. These products cure rapidly, molding cycles of 4 to 5 minutes generally being sufiicient at 140 C. Molding temperatures of C.l60 C. can be used, although the temperatures of C.-l50 C. are preferred; When aconventional molding catalyst such as glycolic acid is added to the dry molding composition, a cycle of only 2 minutes at 140 C. is sufiicient for complete curing. The flow characteristics of these molding compositions are in general superior to those of commercially available urea-formaldehyde molding compositions and the molding pressures required are generally lower. For example, pressures as low as 500 lb./sq. in. are satisfactory for some of the compositions of this invention, whereas pressures of LOGO-3,000 lb./sq. in. are generally required for the commercial resins. The toughness of the molded resins or this invention is somewhat greater than that of commercial thermosetting resins, including the urea-formaldehyde, melamine-formaldehyde and phenolformaldehyde resins.

The resins of this invention are particularly This ising more than 20 cycles of'a'lternate immersiorrin boiling water and air drying without showinganyevidence of crazing or cracking. Furthermore,

The cellulose-filled from 70% to 98% of their flexural strength after being subjected to from 8 to 22 such cycles. On the other hand, conventional urea-formaldehyde resins show excess crazing and cracking after 1 10 ties of paper, lose.

By way of illustration, a resin suitable for applying to paper pulp in the beater prior to formato 4 such cycles, and the test specimens in most tion of the paper sheet in order to form paper cases are too weak to test for flexural strength having h Strength, is P pa d a oll ws! after such exposure. Even the commercial T0 ahexamethylenediamine-modified urea-formmelamine-filled resins, which are known to be de yde resin de' y e process defined P more water resistant than urea-formaldehyde u Y containing 0 o es o o alde yde D resins, generally show slight crazing and crack- R1016 of urea, mole of diamine D mole of ing after 3 to 4 cycles of alternate immersion in urea d heated at in e presence of boiling water and air drying. Further, the p-toluenesulfonic acid catalyst until a pH of 6.5 melamine resins subjected to 5 to 8 cycle of has been reached, is added another 0.04 mole, per this type retain only-40% to 60% of their original e of e of m e amine in the fleXural strength. Similar advantages are exform of its monosalt of acetic acid. The resin is hibited by the diamine-modified urea-formalde-- then heated at 70 C. until the pH reaches 5.0-5.5, hyde resins of this invention in accelerated a out 15 i s being requirede resulting weathering tests, outdoor exposure, and heat q us resm 80111131011 s Concentrated y e ptreatment tests. The following Table I sumoration to a solids content of 95 -100%. Three marizes the results of certain comparative tests parts of this resin is added to 100 parts of paper of the resins of this invention and. several compulp di persed in Wa er in a beater, and, after mercially availabl resin beating until the resin is uniformly distributed,

Table I fig gggg of Water Resistance Flexural -Mo1ded Product Pressure/ 1Slt-r/ength, v

. S 55533 5 3, q Cycles Withstood f fij gf jf min.

Products of Examples:

II 1, 000/140 5 4,000 s+.... 10,600.

V: 2, 000 140 5 15, 200 22+ 14,900. Commercial Urea-Formaldehyde 3, 000/140/5 12,300 1 (Slight crszing) Resin. 22Exeessive crazing) less than 500.

C iilrnrinerRcialMelamine-Forma1de- 1,000/140/5 14,000 2 Slight crazing) 7,300 afterficycles.

1 One cycle consists of 1-2 hours immersion in boiling water followed by air drying for 24 hours. i The number of cycles noted indicates the number of such cycles withstood w1thout showing any evidence of cracking or crazing.

I Flexnral strength determined on molded bar after it had been sub wetting and drying indicated in the column to the left.

The condensation products of this invention are particularly valuable for many uses other than as molding compositions. Either in the presence or absence of fillers, they are useful as bonding agents, textile modifying agents, adhesives, baking enamels, and the like. For these uses resins having the higher ratios of formaldehyde to urea, e. g., 2.0-2.5 moles of formaldehyde per mole of urea, are generally preferred.

These resins are capable of producing high wet strength paper by spraying the resin solution of pH 5.0 to 6.5 on to paper and then drying the treated paper. The resins are also useful as binders for non-woven fabrics and in making surface laminates of impregnated paper.

In some instances Where the water-resistant resins of this invention are to be applied to cellulosic material to improve the water resistance of such material, especially where the resin is to be added to paper pulp in the beater prior to formation of the paper sheet, it is advantageous to introduce ionically charged groups into the resin in order to increas the affinity of the resin for cellulose. This can be done by heating the final resin solution prepared in accordance with this invention with a relatively small proportion of a polyamino compound, especially a primary alkylene diamine of the type used in forming the resin, alone or in the form of a partial or complete salt of an acid until the pH of the resin reaches 5.0 to 5.5. Such modified resins are substantive to cellulose and are useful in modifying the properject to the number of cycles of alternate the pulp is formed into sheets of paper which are then dried. The resulting paper has a wet bursting strength of 50-60% of its dry bursting strength.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The invention claimed is:

1. A condensation product obtained by heating in aqueous medium at less than about C. until a clear solution having a pH between 5.0 and 6.5 is formed, urea, and per mole of urea, 1.5 to 2.5 moles of formaldehyde, and 0.03 to 0.12 mole of a primary alkylene diamine containing from 4 to 10 carbon atoms, inclusive, and in which the primary amino groups are separated by at least 4 carbon atoms, and an acid catalytically active for the condensation of urea with formaldehyde in an amount stoichiometrically equivalent to 2.5% to 12.5% of said diamine, the proportion and character of said acid being such that the pH of said aqueous medium is lowered to at least 6.5 upon heating.

2. Product as set forth in claim 1 wherein said primary alkylene diamine is hexamethylenediam1ne.

3. Product as set forth in claim 2 wherein said acid is p-toluenesulfonic acid.

4. A condensation product obtained by heating textiles, and other forms of cellu in aqueous medium at less-.thanaboutfiS" C. until a clear solution having a pH between 5.0 and 6.5 is, formed, urea, and per mole of urea, 1.6 to 2.0 molesof formaldehyde, and 0.06to 0.09 mole of a primary alky-lene diamine containing from 4 to carbon atoms, inclusive, and in which the primary amino groups are separated by at least4 carbon atoms, and anacid catalytically active-for the condensation of urea with formaldehyde in an amount stoichiometrically equivalent, to 2.5%, to 12.5% of said diamine, the proportion and character of said acid being such that the pH of saidaqueousmedium loweredto at least 6.5 upon heating.

5. Product as set forthin claim 4 wherein said primary alkylene diamine is hexamethylenediamine.

6. Product as set forth -.incl a im 5 wherein said acid is p-toluenesulfonic acid.

7. A molding compound comprising the condensation product set forth in claiml intimately admixed with to 50%, by weight of said molding compound, of a cellulosic filler.

8. A molding compound comprising the condensation product set forth in claim 4 intimately admixed with to 40%, by weight of said molding compound, of alpha-cellulose.

9. Process of preparinga-condensation product which comprises heating at less than about 85 C. in an aqueous medium urea,a nd .l?.er mole of urea, 1.5 to 2.5 moles of formaldehyde, and 0.03 to 0.12 mole of a primary alkylene diamine containing from 4 to 10 carbon atoms, inclusive, and in which the primary amino groups are separated by at least 4 carbon atoms, and an acid 'catalytically active for the condensation of urea with formal-1 dehyde in an amount stoichiometrically equivalent to 2.5% to 12.5% of said diamine, until a clear solution having a pH between 520 and 6.5

is formed, the proportion and character of said.

acid being such that the pH of said aqueous medium is lowered to at least 6.5 upon heating.

7 10. Process as set, forth in claim-9 wherein said primary alkylene diamine is hexamethylenediamine.

11. Process as set forth in claim 10 wherein said acid is p-toluenesulfonic acid.

12. Process of preparing a condensationprod uct comprising mixing urea and formaldehyde in a ratio of 1.6 to 2.0 moles of formaldehyde ncl? mole of urea in a quantity of water amounting to at least 15% by combined weight of the ureaand formaldehyde, adding thereto 0.0.6 .to 0.(I9- mole of .a primary alkylene diaminecontaining from 4 to 10 carbon atoms, inclusive, and in whichthe primary amino groups are-separated :by at least 4 carbon atoms, and thenadding-thereto an acid catalytically active for the condensation of urea with formaldehyde in an amount .stoichiometri-- cally equivalent to 2.5% to 12.5% of. said diamine, and heating said mixture atabout C. to 15C..

until a clearsolution having a pH between 5.0.. and.

6.5 is formed, the proportion and character of said acid being such that the pH of; saidmixture is lowered to at least 6.5 upon heating.

13. Process as set forth in claim 12 wherein said primary alkylene, diamine, is. hexamethylenerdiamine.

14. Process as, set forth in claim 13 wherein said acid is p-toluenesulfonic acid.

WILLIAM ROBERT 'M'c'CLELLAN.

References Cited in the file of this patent UNITED STATES PATENTS .Number Name 'Date 2,334,545 Df'Alelio Nov. 16, 19,43 2,354,671 Eastes .-Aug. 1,1944 2,371,997 Hoover Mar. 20, 16945. 2,485,485 Dudley Oct. =18, 1949 FOREIGN PATENTS Number Country Date 572,245, Great Britain. Sept.'28,.1-9.45 

1. A CONDENSATION PRODUCT OBTAINED BY HEATING IN AQUEOUS MEDIUM AT LESS THAN ABOUT 85* C. UNTIL A CLEAR SOLUTION HAVING A PH BETWEEN 5.0 AND 6.5 IS FORMED UREA, AND PER MOLE OF UREA, 1.5 TO 2.5 MOLES OF FORMALDEHYDE, AND 0.0O TO 0.12 MOLE OF A PRIMARY ALKYLENE DIAMINE CONTAINING FROM 4 TO 10 CARBON ATOMS, INCLUSIVE, AND IN WHICH THE PRIMARY AMINO GROUPS ARE SEPARATED BY AT LEAST 4 CARBON ATOMS, AND AN ACID CATALYTICALLY ACTIVE FOR THE CONDENSATION OF UREA WITH FORMALDEHYDE IN AN AMOUNT STOICHIOMETRICALLY EQUIVALENT TO 2.5% TO 12.5% OF SAID DIAMINE, THE PROPORTION AND CHARACTER OF SAID ACID BEING SUCH THAT THE PH OF SAID AQUEOUS MEDIUM IS LOWERED TO AT LEAST 6.5 UPON HEATING. 